Re: Development Question

[Pieter Palmers <pieterp@joow.be>]

M. Gagnon wrote:
> This is interesting, Pieter, however my app already has the knowledge of 
> notes and events, the only reason i had midi bytes was because i converted 
> the events into bytes because then i could make them play using a single 
> function on mac.
> 
> Apparently on Linux/Alsa it's not this way, so i should probably learn how 
> to put a serie of events in a sequence and then play it. The most recent 
> sample of this i found was dated '2002' and didn't work, and my own attempts 
> with the documentation didn't either.
> 
> I am already able to send events directly. Where can i find recent 
> infomation on how to schedule them in a queue and play them after?
I found the doxygen docs that come with alsa-devel sufficient.

What you have to do is convert your own 'events' into ALSA seq events, 
and then use the snd_seq_event_output function. Things as timestamps 
etc... are properties of ALSA seq events, and can be set using 
snd_seq_event_* functions.


Pieter

PS: One tricky thing if you use multiple ports is that the port an event 
should be sent to is also a property of the event.


> 
> thanks
> 
> 
>> From: Pieter Palmers <pieterp@joow.be>
>> To: "M. Gagnon" <fire_void@hotmail.com>
>> CC: alsa-devel@lists.sourceforge.net
>> Subject: Re: [Alsa-devel] Development Question
>> Date: Sat, 17 Mar 2007 22:36:31 +0100
>>
>> M. Gagnon wrote:
>>> Hi, i am now trying to port an application to linux using Alsa. At some 
>>> point, i have midi bytes as char* and i have to play them. This is exactly 
>>> the same data you'd find in a file, expect that it's in memory instead. 
>>> How is that possible?
>>>
>>> If this is not possible, i could always take any help on playing midi 
>>> using sequencers I looked at the docs, i found a few samples, but they 
>>> seemed to be outdated and the one that could interest me segfaulted. After 
>>> i debugged it and fixed the segfault, it played nothing... (and i'm sure 
>>> my midi is configured correctly BTW, pmidi works and i also succeeded in 
>>> getting single notes to play)
>> This is how I do playback in the freebob backend for jack:
>>
>> for (s=0;s<samples_read;s++) {
>>   signed int *byte=(buff+s);
>>   snd_seq_event_t ev;
>>   if ((snd_midi_event_encode_byte(
>>          port->parser,(*byte) & 0xFF, &ev)
>>        ) > 0) {
>>       // a midi message is complete, send it out to ALSA
>>       snd_seq_ev_set_subs(&ev);
>>       snd_seq_ev_set_direct(&ev);
>>       snd_seq_ev_set_source(&ev, port->seq_port_nr);
>>       snd_seq_event_output_direct(port->seq_handle, &ev);			   }
>> }
>>
>> you can check the freebob_driver_midi_* functions in the freebob jack 
>> backend for more detail.
>>
>> Pieter
>>
> 
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